Expanding production and uses of hydrocarbon fluids both as fuel gases and as raw materials for various purposes create a definite problem in providing large storage facilities for these fluids. Sometimes long storage of some hydrocarbons, such as propylene, is required to provide capacity for variable demands.
Salt storage caverns have provided a convenient answer, easily handling the frequently several hundred pound per square inch storage pressures required, and providing relatively economical large storage capacities to provide response to seasonal peak load demands and requirements, and corresponding storage during seasonal slack periods.
In a cavern formed in a salt strata, a pool of brine generally occupies the lower portion of the cavern volume, and the stored hydrocarbon fluid occupies the upper portion. Thus, the cavern always is maintained full. An access bore is provided, relatively small in diameter, with dual fluid passages so that fluid handling means at the surface provide capability for brine to be pumped in or out of the lower area of the cavern, and hydrocarbon fluid then can be taken from the upper area. Hydrocarbon product is added to storage by pumping into the cavern under sufficient pressure to displace brine therein back to the surface. Displaced brine is maintained at ground level in a brine pit or reservoir, and then is returned to the salt cavern to replenish the brine volume as hydrocarbon fluid is retrieved. Precautions are taken to assure that the brine in and out is always salt-saturated to avoid enlarging the brine cavern and/or to avoid salt dropout at the surface due to changes in temperature.
However, with a "wet" stored hydrocarbon, other problems exist. The hydrocarbons from pipeline or production for storage normally is dry. It becomes wet in the cavern. Upon retrieval, it must be re-dried. Moisture in transmission pipelines is undesirable. Re-drying is a relatively expensive procedure requiring desiccant beds to dry the retrieved wet hydrocarbon, periodic regeneration with hot gases which is an energy-consuming step, and so on. However, this is and has been the current practice.
Needed is a method and apparatus to wet store hydrocarbon fluids, and yet retrieve the hydrocarbon fluids relatively dry, in an energy efficient manner.